In the art of metal-oxide-semiconductor field-effect transistors (MOSFET) built on semiconductor substrates, there is a constant push to improve the MOSFET performance and efficiency. This process includes scaling down the size of these MOSFET devices. As MOSFET devices are scaled to smaller dimensions, the silicon dioxide gate dielectric layers that are conventionally used in these devices become too thin and have to be replaced by high-k gate dielectric materials. Unfortunately, there are some drawbacks to the use of high-k dielectric materials. For example, after a high-k dielectric material is deposited on the semiconductor substrate, subsequent thermal processing unintentionally causes an interfacial layer to form at the interface between the high-k gate dielectric layer and the substrate. This is because the thermal processing causes oxygen in the high-k material to react with silicon in the substrate, thereby forming the interfacial silicon dioxide layer. This silicon interfacial layer has a low dielectric constant that adversely impacts the effective dielectric constant of the gate dielectric stack.
Another issue with the use of high-k dielectric materials is that phonons in the high-k dielectric material tend to couple with the field of electrons in the channel region of the MOSFET device. This coupling between the high-k phonons and the field of electrons degrades device mobility. Accordingly, improvements to the gate dielectric layer are needed to enable further scaling of MOSFET devices.